摘要:

The magnetic properties of theFexMn0.7−xAl0.30(0.40⩽x⩽0.58)alloy series have been investigated by means of57FeMo¨ssbauer spectroscopy and ac magnetic susceptibility measurements. From our data, we propose a magnetic phase diagram for the system which is adequately reproduced by a diluted and random-bond Ising model which was analyzed on the basis of the mean-field renormalization-group method. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366500

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Sm10Fe90−xTixalloys(x=0, 1, 3, 4, 5, 6, 8, 10) were prepared by rapid quenching and sequent annealing. Structural transformations from amorphous, metastable-to-equilibrium phases, and magnetic properties of their nitrides were systematically investigated. ACaCu5-type metastable phase was formed for0⩽x⩽10as the crystallization of the amorphous alloys occurred below 700 °C. TheCaCu5-type structure is transformed into aTbCu7-type one with increased annealing temperature (above 700 °C). These alloys have different structures includingTh2Zn17type for0⩽x⩽3,TbCu7type for3<x<6,andThMn12type for6⩽x⩽10,at high annealing temperatures (above 950 °C). Nitrogenation was carried out at 460 °C for 6 h. The best hard magnetic properties are obtained after nitriding forx=3.It givesiHc=17.6kOe,4&pgr;Mr=7.7kG, and(BH)max=6.8MGOe for theTbCu7-type phase andiHc=8.6kOe,4&pgr;Mr=8.4kG, and(BH)max=10.2MGOe for theCaCu5-type one. Although the coercivity of theCaCu5-type phase is lower than that of theTbCu7-type one, enhanced remanence of the former has been observed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366501

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have studied the effects of surface crystallization on the magnetic properties ofFe80B20amorphous alloys. The surface magnetic properties have been studied with magneto-optic Kerr measurements, while those of bulk with a vibrating sample magnetometer. This study reveals that surface crystallization is similar to the bulk process but occurs at a lower temperature. At variance with previous results on other iron-based amorphous alloys the surface crystalline layer does not induce bulk magnetic hardening. Furthermore, both the remanence to saturation ratio and the bulk magnetic anisotropy do not show appreciable variations after the formation of the surface crystalline layer. The Curie temperature of the surface layer is lower with respect to the bulk of the sample. These effects can be explained by a lower boron concentration in the surface region of the as-cast amorphous alloy. Measurements of the chemical composition confirm a reduction of boron concentration in the surface region. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366502

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A systematic study of the magnetic properties of the manganitesLn0.5(A,A′)0.5MnO3(A,A′=Ba,Ca, Sr) has been carried out. The variations ofTCandTNvs two parameters, the average size of the interpolated cations⟨rA⟩and the mismatch effect represented by the variance&sgr;2,have been studied for the series of manganitesLa0.5(A,A′)0.5MnO3,Pr0.5(A,A′)0.5MnO3,Nd0.5(A,A′)0.5MnO3andSm0.5(A,A′)0.5MnO3(A,A′=Ba,Ca, Sr), involving at most three different cations on the perovskite A site. The results obtained for other(Ln, Ln′)0.5Sr0.5MnO3(Ln, Ln′=Gd, Sm Y, Pr)have been taken into consideration. A&sgr;2−⟨rA⟩diagram has been established, which displays the different types of magnetic behaviors that can be exhibited byLn0.5A0.5MnO3manganites, i.e., when the temperature is decreasing, either a paramagnetic (PM) to ferromagnetic (FM) transition, or PM to FM followed by FM to antiferromagnetic transitions, or a PM to weak ferromagnetic transition. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366543

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have studied ultra-thin Co/Au(111) films with perpendicular magnetic anisotropy by means of spin-wave Brillouin scattering. The ultra-thin Co films with thicknesses from 1 to 7 monolayer (ML) were grown by molecular beam epitaxy on 1 ML Au underlayers without intentional substrate heating. With 2 or more MLs of Co, spin-wave excitations are clearly observed. We find the magnetic field dependence of the spin-wave energy can be quantitatively explained by a calculation including out-of-plane magnetization due to uniaxial perpendicular magnetic anisotropy. The first-order perpendicular anisotropy constant systematically increases as the Co thickness decreases from 7 to 3 ML. The second-order perpendicular anisotropy constant is much smaller than that expected in Co(0001) bulk and also increases as the Co thickness decreases. The physical origin of the thickness dependence of the perpendicular anisotropy is discussed. We find the field dependence of the scattering intensity is different between Stokes and anti-Stokes processes. Finally, with 2 ML of Co, significant broadening of the spin-wave spectrum is observed, as well as the degradation of the perpendicular anisotropy. We believe this is the result of the effect of magnetic inhomogeneities due to the structural imperfections. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366503

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

InterstitialY2Fe17−xMxCycompounds, withM=Alor Si andx⩽2,y⩽1,were investigated by57FeMo¨ssbauer spectroscopy at room temperature. In the analysis of the spectra, the preferential occupation by Al or Si of the Fe(12k)sites in the hexagonalR2Fe17phase was taken into account. The hyperfine parameters variations are discussed on the grounds of local crystallographic details at the inequivalent iron sites, altered by the composition modifications. The low values of the isomer shifts and quadrupole interactions suggest small electronic charge redistribution inY2Fe17−xMxAyas compared toY2Fe17.However, the isomer shift variations upon Wigner–Seitz cell volume changes evidence for screening and electron transfer effects. In order to provide a more consistent picture of the local effects of interstitial versus substitutional atoms inR2(Fe,M)17Aycompounds, the discussion of the present results is extended to57FeMo¨ssbauer data obtained on the parent compounds and their nitrides. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366504

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The dielectric reliability for polycrystalline and multilayeredBaTiO3thin films has been evaluated using time-zero and time-dependent dielectric breakdown techniques. The histogram of dielectric breakdown for multilayeredBaTiO3thin films showed a typical Weibull distribution in contrast to a random distribution when compared with polycrystallineBaTiO3thin films. The measurement resulted in that the 400 nm-thick multilayeredBaTiO3thin film sustained about105hour-long operation at 1 MV/cm, showing superior properties when compared with polycrystalline. The smaller leakage current level was obtained for a multilayeredBaTiO3film having a relatively thick underlayer of polycrystallineBaTiO3film. The value of the breakdown field was smaller at the thicker multilayeredBaTiO3while the distribution of the breakdown widened for thicker film. Analysis of the roughness for the films confirmed that the field breakdown mechanism (e.g., lowering and spreading) is related to the surface roughness of the topmost layer which varies with the thickness of underlying polycrystallineBaTiO3.The reduced leakage current at the thick multilayeredBaTiO3was due to the presence of a wide transition layer between polycrystalline and amorphousBaTiO3.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366505

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Thin films of silicon nitride of various thicknesses, deposited by radio frequency magnetron sputtering on silicon quartz substrate, have been characterized by laser-induced and frequency scanned photothermal radiometry. Fourier transform infrared spectroscopy was also used to provide a qualitative description of the behavior of the films in the infrared range which shows favourable properties of these coatings to be used in passive cooling applications. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366506

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A two layer model has been developed in order to study the dependence of the photothermal radiometric signal on the optoelectronic and thermophysical properties of a two layer semiconducting sample. In the following theoretical analysis, both thermal and electronic contributions have been used in order to interpret the infrared emission of a semiconducting sample under the influence of a pump modulated laser beam. The potential of the above model towards a quantitative analysis of photothermal radiometric experimental data, for the extraction of thermal and electronic parameters of the semiconducting thin film and substrate, has been examined. Experimental evidence of the quality of this model has also been presented. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366507

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Room temperature absorption and reflectivity data are presented forCd2P2S6andCd2P2Se6crystals in the range of photon energies between 1.6 and 5.5 eV. For both compounds the characteristic feature of the optical absorption is that their absorption edge appears to correspond to an indirect allowed transition with an optical energy gap of 3.06 eV forCd2P2S6and 2.29 eV forCd2P2Se6.An associated phonon energy of 74 meV forCd2P2S6and 50 meV forCd2P2Se6is also deduced. TheCd2P2X6(withX=Sor Se) reflectivity spectra are compared with the early reflectivity spectrum ofZn2P2S6.As observed in previous reflectivity spectra of theHg2P2X6compounds, near the fundamental absorption edges theCd2P2X6reflectivity spectra show a pronounced rise in reflectivity, a feature common to most layered compounds. For photon energies greater than their absorption edges, the reflectivity spectra of both materials look similar to one another and to that ofZn2P2S6.On the basis of these similarities we have adopted the so-called transition metal weakly interacting model and interpreted the spectral structures as direct allowed interband transitions. For both compounds, these electronic transitions are described by a simplified energy-band scheme. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366508

出版商:AIP    

年代:1997

数据来源: AIP